Calcareous grassland is restricted to shallow soils derived from a variety of lime-rich bedrocks such as Carboniferous Limestone which was formed a staggering 350 million years ago. There is an estimated 10,000 ha of upland calcareous grassland in England, with particularly important areas for the habitat in the North Pennines (including the Yorkshire Dales National Park) and Cumbria.
These calcareous grasslands are broadly of two types. The first and least widespread are the blue moor-grass dominated upland grasslands. The more widespread type of calcareous grassland is more lowland in character and dominated by fescues and characterised by the presence of fine-leaved sedges. Richer grasslands may include a common milkwort and common rock-rose and rarely Frog Orchids and Field gentians.
Calcareous grasslands are of very high biodiversity importance in the Yorkshire Dales National Park. Both upland and lowland calcareous grasslands continue to be on the UK list of priority habitats for biodiversity action.
Within Britain this attractive grass species is a northern specialty, and is virtually restricted to the carboniferous limestone areas in northern England. As a result of this dependency upon limestone another common name is popular, Blue Rock-grass.
In the Dales the species is common: in pastures which have thin soil over limestone; in the grykes of Limestone Pavement; and on rocky ledges. As a result of local geology it is most frequent in the southern part of the Dales. In the early spring the hillsides of Wharfedale are often tinged with blue from the nodding grass-heads.
In grassland the species is frequently the dominant grass species growing with other calcareous species including Common rock-rose (Helianthmum nummularium).
The bedstraws were so-called because they were formerly used with straw for stuffing mattresses. Limestone bedstraw is a small mat-forming herb with very small white flowers and whorls of small leaves with a bristle-like point at the end of each leaf and backward pointing prickles.
In the British Isles this species is locally frequent on calcareous grasslands and rocky habitats north of a line from the Severn to the Humber estuaries. In the Yorkshire Dales National Park limestone bedstraw is very common and can be seen flowering between June and July on calcareous grasslands alongside blue moor-grass.
The Common rock-rose’s Latin name is Helianthemum which translates as ‘sun-flower’. This is because the flowers react to the sun and will open fully in bright sunshine.
Its colours range from the more common bright yellow through to various shades of orange. Growing close to the ground, this evergreen shrub produces a mass of short-lived flowers during summer.
In the Yorkshire Dales National Park, common rock-rose can be found on limestone grassland and in crevices between limestone rocks. In the summer, the bright yellow flowers are a common sight in the limestone grasslands of the Craven District of the National Park.
The Common rock-rose is an important part of the eco-system and provides a food source for the larvae of several species of moth and butterfly including the northern brown argus butterfly.
Common Milkwort likes short-turf, calcareous grassland. Mostly its flowers are blue but pink- and white-flowered forms occur. A closely related species – Heath Milkwort (Polygala serpyllifolia) – thrives on the calcium-deficient soils that Common Milkwort avoids. Both species flower between May and August. A third species that is quite rare is found in wet limestone grassland in the Craven district and in Teesdale. This is Dwarf Milkwort (Polygala amarella).
In mid-summer a thick carpet of Wild thyme can create an aroma that is reminiscent of the Mediterranean. The leaves of Wild thyme contain the volatile oil thymol, which has antiseptic and preservative qualities. The herb has also been used to flavour foods although is not as strongly flavoured as the cultivated thyme (T. vulgaris) which is one of Britain’s best-known and most widely used culinary herbs The essential oil gathered from Thyme plants is also used in toiletries to scent soaps and perfumes.
In the Dales the plant grows on limestone rocks, limestone pavement, roadside verges and on short, dry, and generally calcareous grassland, to above 400m. This low evergreen shrub has a rambling growth form and is known for supporting insects and attracts bees and butterflies.